The present invention relates to reactor vessels with a reactor core enclosed in a core shroud and more particularly, to an apparatus for inspection of a reactor vessel.
Inspection of the interior of a reactor vessel typically includes the systematic inspection of weld joints in the reactor vessel and pipe sockets etc. Usually, an end effector comprising inspection members in the form of, for example, cameras, ultrasonic probes or the like is moved into the reactor vessel with the aid of special devices. These devices generally include a trolley, which is movable on the exposed upper flange of the vessel, provided with traversing wheels and a drive means. The trolley supports a support mast which is immersed into the reactor vessel substantially parallel to the vertical axis of the reactor vessel. The support mast supports the end effector which may be moved with the aid of a drive member.
The device disclosed in U.S. Pat. No. 4,585,610, is well known in the art and includes a trolley with three or four wheels, which supports a support mast centrally insertable in the reactor vessel. Inspection of the vessel wall weld joints is accomplished by means of ultrasonic probes, which make contact with the vessel wall. However, the inspection depth is often limited by reactor components located at the wall of the vessel such as feed water spargers and/or core spray spargers which are not normally dismantled during inspection. Consequently, using this inspection technique weld joints and reactor components located towards the bottom portion of the reactor vessel are not accessible to inspection.
It is also well known in the art to place the ultrasonic probes on an extension mast which is fixed to the lower part of the support mast and movable in the radial direction of the vessel. However, the support mast is lowered into the reactor vessel at such a large distance from the its wall that the support mast and the extension mast clear the feed water spargers. When the extension mast has cleared the spargers, the extension mast, by means of the trolley, is moved radially towards the vessel wall below the feed water spargers and also below any core spray spargers which may exist. Although this technique permits a certain increase in the available inspection depth, the inspection depth is limited by the fact that the extension mast cannot be made longer than the axial distance between the feed water spargers and the core shroud cover. In order for the extension mast of this conventional system to clear the feed water spargers, the extension mast must protrude within the annular space formed by the projection of the core shroud cover and the vessel wall. However, the extension mast can only be inserted into the reactor vessel to a point where it contacts the core shroud cover. Therefore, particularly in reactor vessels in which the distance between the core spargers and core shroud cover is relatively short, the space between the reactor vessel and the core shroud which is available for inspection is limited with use of the conventional inspection system.
It is therefore an object of the present invention to provide an apparatus for inspection of a reactor vessel which is capable of being inserted into the lower portion of the annular space between the core shroud and the wall of the reactor vessel.
It is also an object of the present invention to provide a reactor inspection apparatus which enables inspection of a greater area of the reactor vessel by providing for increased radial, tangential and axial movement of the end effector relative to the reactor vessel wall.